A) Field of the Invention
This invention relates to an apparatus and a method for manufacturing a semiconductor device, and more specifically relates to an apparatus and a method for growing a nitride semiconductor crystal film by using a metal organic chemical vapor deposition (MOCVD) method.
B) Description of the Related Art
A metal organic chemical vapor deposition (MOCVD) method is one of chemical vapor deposition methods and used mainly for growing semiconductor crystal.
FIG. 6 is a schematic diagram showing an example of a conventional semiconductor manufacturing apparatus 200.
For example, the semiconductor manufacturing device 200 consists of a reaction chamber 1, a susceptor 2, a substrate heater 3, a reactant gas supplying unit 4, a vacuum (exhaust) pump 5, a substrate rotating unit 7, a subflow gas source 8, a subflow gas controller 50, and a baffle plate (subflow-directing unit) 51.
The reactant gas supplying unit 4 consists of, for example, a reactant gas source, a mass flow controller (MFC), reactant gas nozzle 4p, etc. and supplies reactant gas such as trimethyl gallium (TMG), ammonia gas (NH3), etc. via a reactant gas nozzle 4p placed near the susceptor 2 in the reaction chamber 1. The supplied reactant gas is pyrolysed in the reaction chamber 1 and forms a desired material film on a growth substrate 6 placed on the susceptor 2 supported by a rotating shaft 2s in the reaction chamber 1. The rotating shaft 2s is connected to a substrate rotating unit 7 and rotates in a predetermined direction. Therefore, the growth substrate 6 placed on the susceptor 2 also rotates in the predetermined direction.
The baffle plate (subflow-directing unit) 51 emits subflow gas 52 supplied from the subflow gas source 8 via a subflow gas controller 50 onto an upper surface of the growth substrate 6. The subflow gas source 8 supplies inactive gas such as H2, N2, etc. as the subflow gas which does not include reactant gas, and the subflow gas controller 50 controls an amount of flow of the subflow gas. The baffle plate 51 defines a flowing direction of the subflow gas 52 and has holes functioning as subflow gas emitting nozzles tilted with a predetermined angle (e.g., 90 degrees) to the upper surface of the substrate 6. From those holes the subflow gas 52 is emitted onto the upper surface of the substrate 6 with the determined angle. The subflow gas 52 brings the reactant gas into contact with the upper surface of the substrate 6 for spreading the reactant gas evenly all over the upper surface of the substrate 6 without being diffused in the reaction chamber 1 by thermal convection or the likes.
The reactant gas and the subflow gas 52 are exhausted from the reaction chamber 1 by the vacuum pump 5 via the exhaust port. A cleaning mechanism (not shown in the drawing) for capturing hazardous waste in the exhaust gas is configured before the vacuum pump 5 because the exhaust gas includes massive reaction byproducts and residual substances. Moreover, special equipment for safety disposal (not shown in the drawing) is configured at the end because the exhaust gas tends to include toxic waste such as arsenic or the likes.
FIG. 7 is a graph showing relationships between a distance from an edge of a substrate and a growth rate when nitride semiconductor crystal films are grown by the conventional semiconductor manufacturing apparatus 200. In this graph the distance from one edge of the growth substrate 6 in the unit of [mm] is on the horizontal axis, and the growth rate for one hour in the unit of [μm/hour] is on the vertical axis. A diameter of the growth substrate 6 was 50 mm.
Good growth of semiconductor films could be obtained in a range of 20 mm to 30 mm from the edge, that is, near the center (about 25 mm from the edge) of the growth substrate 6, and growth of semiconductor films which could be used for an LED could be obtained in a range of 10 mm to 40 mm from the edge. However, in a region closer than about 10 mm from the edge and in a region further than about 40 mm from the edge (in a 10 mm wide area from the outer periphery of the growth substrate 6), film thicknesses became too thick comparing to the center and so it could not be used for an LED.
As in the above, in order to prevent the growth rate in the outer periphery of the growth substrate 6 from becoming larger than the growth rate in the center of the growth substrate 6 and to prevent the thickness of the outer periphery from becoming thicker than that in the center, it has been suggested that gas is emitted for removing a part of reactant gas in the outer periphery (see Japanese Patent No. 4096678).
Japanese Patent No. 4096678 (hereinafter patent document 1) discloses a technique using first subflow gas (pressing gas) emitted with an angle of 45 to 90 degrees for bringing reactant gas into contact with a surface of a substrate and second subflow gas (removing gas) for removing the reactant gas in a periphery of the substrate. A nozzle for the second subflow gas is emitted at a right angle or slanted to an emitting direction of the reactant gas in an in-plane direction of the growth substrate and to an opposite direction to a rotating direction of the substrate.
In the conventional technique according to the patent document 1, the nozzle for the second subflow gas is placed in front of the reactor. That is, the nozzle for the second subflow gas and a nozzle for the reactant gas are arranged to make their emitting angles to the surface of the substrate 6 same with each other (placed in parallel to the surface of the substrate); therefore, a large space around the substrate becomes necessary.
Because the nozzle for the second subflow gas is placed in parallel to the surface of the substrate, the second subflow gas spread in a direction in parallel to the surface of the substrate 6 and a component flowing in an opposite way to a flow of the reactant gas may be generated and cause generation of spiral flow which obstructs reproducibility.
Moreover, the first subflow gas and the second subflow gas are emitted to the same place so that the second subflow gas obstructs the flow of the first subflow gas and the effect of the first subflow gas, brining the reactant gas into contact with the substrate, is reduced.